Add warning message on new Copay version

We are using the last github tag for comparing the versions.

The alert shows only on major and minor miss match, making the message more clear on the first one. The message is fixed and can't be dismissed by the user, but still let them operate the wallet as usual.

VERSION = MAJOR.MINOR.XX

Closes #473

![screen shot 2014-06-02 at 16 55 47](https://cloud.githubusercontent.com/assets/279449/3152602/6425f890-ea90-11e3-9b30-2efacce9f0dc.png)
![screen shot 2014-06-02 at 16 57 05](https://cloud.githubusercontent.com/assets/279449/3152606/668306a0-ea90-11e3-941d-2f9a490bfca9.png)